Syria's foreign ministry has claimed the year-old revolt to topple President Bashar al-Assad is over amid reports that the army is continuing to shell opposition areas.

The government statement came as rebels maintained they would not cease fire until tanks, artillery and heavy weapons were withdrawn.

"The battle to topple the state is over," ministry spokesman Jihad al-Makdissi told government channel Syria TV. "Our goal now is to ensure stability and create a perspective for reform and development in Syria while preventing others from sabotaging the path of reform."

Washington and Gulf Arab states urged the UN and Arab League's peace envoy Kofi Annan to set a timeline for "next steps" if there was no ceasefire, and Saudi Arabia repeated a call for rebels to be armed. Annan, whose mission has so far failed to bring respite to the bloodshed, has said neither measure would be helpful.

Syria also said it would keep its forces in cities to "maintain security" until it was safe to withdraw them in line with the peace deal, which Assad has said he accepts. Annan's plan says the army must stop violence immediately and be the first to withdraw forces.

"We cannot accept the presence of tanks and troops in armoured vehicles among the people," a spokesman for Free Syrian Army commanders inside Syria said. "We don't have a problem with the ceasefire. As soon as they remove their armoured vehicles, the Free Syrian Army will not fire a single shot," Lieutenant Colonel Qassim Saad al-Din told Reuters.

A rebel officer in Damascus said separately: "When Assad's gangs stop the shelling and killing of civilians, then our leaders can issue an order to stop operations and we will commit to it to show our good intentions."

Opposition activists said 25 people had been killed and reported signs of torture on five of the bodies, including two children.

A protest singer in Kafr Ruma was killed when his house was raided, activists said. A young man and his sister were shot dead when state forces stormed their village, and a man died of gunshot wounds inflicted during a protest in Damascus, the activists added.

Artillery and mortars pounded a pro-opposition part of Homs city, killing one. Ten deaths were reported in Homs province. "Mortars are falling every minute and the sounds of explosions are shaking the [Khalidiya] neighbourhood," the Syrian Observatory for Human Rights said.

But Damascus appears to have the upper hand following army victories over rebel strongholds in the cities of Hama, Homs and Idlib, and Assad's acceptance this week of Annan's plan that does not demand he step down.

The political opposition remains divided and prospects of western-led military intervention are close to zero. Assad's opponents have not yet formally accepted the UN plan.